Fuel cells are poised for future power generation, providing an efficient and clean alternative to current power sources, especially portable or on-site power generation. Polymer electrolyte membrane fuel cells (PEMFC) are especially equipped to power the automobiles of the future as they operate at low temperatures and have shown to have high power densities (over 2 kW/1 and 1 W/cm2).
As a single fuel cell will generally not provide enough power for the efficient operation of automobiles or portable electronics, generally a plurality of fuel cells are stacked to aggregate their power generation. The fuel cells are each separated by a bipolar plate, which electrically connects the fuel cells together, combining their power output, while also allowing the reaction gases and reaction products to pass to and from the fuel cells. U.S. Pat. No. 4,175,165, hereby fully incorporated by reference, describes one example of bipolar plates used in a fuel cell stack. Bipolar plates allow multiple fuel cells to be stacked together, aggregating their power, in a compact efficient design, minimizing size and electrical resistance across the fuel cell stack.
Bipolar plates in a fuel cell stack provide structured surfaces to guide reaction gases and reaction products through defined channels as they enter and leave the fuel cells while also electrically connecting the fuel cells. These bipolar plates therefore need to be gas impermeable, electrically-conductive, corrosion resistant, light-weight, strong, flexible and economical to manufacture. In particular, bipolar plates must withstand the corrosive effects of the cathodes of adjacent fuel cells, the corrosive nature of the reaction gases and reaction products (humidity), any heat transfer fluids used to cool the fuel cell stack, and combinations thereof.
Bipolar plates used today generally use machined graphite plates, that are electrically-conductive, corrosion resistant and gas impermeable. Unfortunately, graphite plates are expensive, inflexible and succumb to brittle fracture. Attempts have been made to use lower cost and more durable metals such as stainless steels, aluminum, nickel, titanium and other alloys, which can be made gas impermeable. However, these materials are susceptible to severe corrosion due to the acidic conditions of fuel cells, such as PEMFCs.
Some attempts have been made to provide metallurgical coatings to protect the base metals, but these have proven to be costly and time consuming. Recently, there have been efforts to develop a bipolar plate out of polymer-composites, however these polymer-composite plates do not have sufficient gas impermeability, nor do they provided suitable electrical conductivity. Furthermore, polymer-composite bipolar plates are prone to failure at temperatures over 80° C.
Therefore, there exists a need for a gas impermeable, electrically-conductive, corrosion resistant, light-weight, strong, flexible and low cost material for use in applications such as bipolar plates for fuel cell stacks.